U.S. federal investigators say a train that derailed Monday in the northwestern U.S. state of Washington was traveling at 129 kilometers per hour on a stretch of track where the speed limit was 48 kilometers per hour.

The train went off the tracks on a curve south of Seattle, sending some of its cars onto a busy interstate highway below and killing at least three passengers.

National Transportation Safety Board member Bella Dinh-Zarr told reporters that investigators have examined an event data recorder recovered from one of two locomotives on the train, which was making its first-ever run along a faster new route.

Dinh-Zarr said the NTSB team will really begin its work at the crash site on Tuesday, and that investigators will be interviewing crew members to determine what went wrong and why.

"It's a very complicated accident," she said.

Typically NTSB teams are on-site for seven to 10 days before analyzing the information they gather and issuing a report on the findings.

In addition to those killed, local officials said more than 100 others were injured.

Washington State Patrol spokeswoman Brooke Bova said five vehicles, plus two semi-trailer trucks, were hit by the derailed train cars. Some motorists were injured but none died, according to authorities.

Amtrak said 80 passengers and five crew members were on board the Cascades train 501, part of a newly expanded service between Seattle, Washington, and Portland, Oregon.

This photo provided by Washington State Patrol shows an Amtrak train that derailed south of Seattle on Dec. 18, 2017.

Herb Krohn, Washington state legislative director for the former United Transportation Union Sheet Metal Air Rail Transportation union that represents workers there, said the new train route opened after several years of work and cut about 15 minutes off the ride time from Seattle to Portland. He expressed concern for the families of the passengers and crew and said the NTSB will look at "absolutely every factor" during its probe.

"It’s a very thorough collaborative process between the federal government and the railroad carriers and railroad labor and they do a really good job at trying to piece these things together and come out with a determination as to the causes as well as possible contributing factors," Krohn said.

He cautioned against jumping to conclusions until there is "credible evidence as to what happened and how we can make sure it doesn't happen again."

The derailment site is about halfway between Olympia, the state capital, and the city of Lakewood.

This aerial image from video provided by KOMO-TV, shows the site of an Amtrak train that derailed south of Seattle on Dec. 18, 2017.

Lakewood Mayor Don Anderson told VOA his city fought against the new Amtrak line, which moved fast passenger trains onto what had been a less-used freight line. He said it was a costly project that provided little transportation benefit, while also creating a risk to pedestrians and vehicle traffic by mixing roads and train crossings.

"We politically and legally took whatever action we could to either stop it or provide for additional safety modifications," Anderson said.

The mayor called Monday's accident "a tragedy for all concerned."

​U.S. President Donald Trump expressed condolences for the victims at the beginning of a speech in Washington Monday.

President Donald Trump speaks on national security, Dec. 18, 2017, in Washington.

"Let me begin by expressing our deepest sympathies and most heartfelt prayers for the victims of the train derailment in Washington State. We are closely monitoring the situation and coordinating with local authorities.

"It is all the more reason why we must start immediately fixing the infrastructure of the United States," he added.

Washington state transportation officials said the section of track where the derailment took place had been outfitted with a safety system known as positive train control, which can slow or stop a train. But the system was "not yet operational or certified for use."

Congress mandated that the nation's railroads implement positive train control after a series of accidents. The legislation calls for the safety upgrades to be completed by the end of 2018, after the railroads won a three-year delay from the original 2015 deadline.

In May 2015, an Amtrak train derailed in Philadelphia as it went into a curve at more than double the posted speed limit. Eight people died in that accident, which investigators blamed on the engineer being distracted by radio conversations between trains and dispatchers about trains being hit by rocks.

The site of the Philadelphia derailment was not equipped with positive train control technology, and the NTSB determined the accident could have been prevented if that system or another form of control had been in place to force the train to follow the speed limit.